ICSH

Please describe your assumptions and/or implementation here. -AJ:

I have only tested the inputs similar to the example usages on the milestones. The program assumes that there is only a max of 100 background processes to save my VM's life... I can handle SIGTSTP and SIGINT but the logic with my SIGTSTP handler had problems with being incorporated to job handling which prevents my bg %<job_id> implementation from being tested. Other than that, the rest of the implementations should work as expected.

Description

main() When launching the program with ./icsh, the interface starts with "Starting IC shell" and then provides the prompt "icsh $ ". This prompt will repeatedly show up with most inputs until the program ends with commands like exit #.

• Both SIGTSTP and SIGINT are handled wotj signal_handler such that they will not stop the main IC shell process.
• Any child process completion will signal check_background_jobs() for "asynchronous" printing.
• Using fgets, the user input is captured as a command and then this is processed with process_cmd().

process_cmd() Commands that were directly told to implement such as echo $?, !!, exit #, jobs, fg %#, and bg %# have their own conditions explicitly. There is a script_mode used here to circumvent the feature shown in Milestone 2. There was an implementation for echo here previously but because it may use Output Redirection, this is now handled with external_cmd() which handles any external command that was not implemented.

• Using the command jobs iterates through the jobs collection and displays the programs along with their statuses. If the status member of the struct was implemented perfectly, the if-statements inside could have been simpler.
• Using the command fg %# checks first if the input Job ID exists, and then properly uses it as fg_process while also waiting for it to finish.
• If successful, using the command bg %# also checks first if the input Job ID exists, and then switches its status while also calling kill(job_pid, SIGCONT) in order to continue the suspended process.
• Anything else is directly passed into external_cmd()

external_cmd() For external commands, the example code for it was used and then modified heavily to support any default bash command, input and output redirection, and background processes.

• The input and output redirection code was inspired from a StackOverflow post, not from the example given.
• Commands meant to be run in the background are identified with their last character '&'.
• Background processes are stored inside jobs using a Job struct that can hold their pid, cmd, and status.
  • indices will be used as the Process ID's that are meant to start at 1
  • cmd is the string that will be displayed when referring to the process
  • status is marked with 1 for Running, and 0 for Stopped

check_background_jobs() This function readjusts the jobs collection whenever a bg_process completes. This allows for "asyncrhonous" printing. This also reduces the number of jobs of course.

signal_handler() Previously, I used signal() instead of sigaction() for Milestone 4 but then changing it to the latter to follow the example worked out fine. However, either my logic fails or I barely understand signal handling which is why it cannot properly suspend a process in order to send it to jobs while Stopped which also prevents with testing bg %#.